In normal, healthy epidermis the continuous production of new stratum corneum is balanced by a well-regulated shedding of corneocytes from the skin surface. Little is known about this desquamation process at the molecular level.
It has been shown by A. Lundstr om and T. Egelrud (J. Invest Dermatol, (1988) 91 340-343; Arch Dermatol Res (1990) 282 234-237; J. Invest Dermatol (1990) 94 216-220) that cohesion between cells in the stratum corneum is dependant on protein structures. These structures must be degraded before cell dissociation can occur.
Furthermore, evidence has been provided to show that cell dissociation is preceded by a degradation of the extracellular parts of desmosomes. (T. Egelrud (1992) European Journal of Dermatology 2 46-49).
A. Lundstr om and T. Egelrud have shown that the stratum corneum contains a protease enzyme--stratum corneum chymotrypsin-like enzyme (SCCE) which may be involved in the process of cell dissociation (desquamation): (Acta Derm Venereol (1991) 71 471-474), and that this enzyme may be involved in desmosomal degradation.
There has been much activity by cosmetic companies to solve the problem of being able to provide a skin care composition which is truly effective against dry flaky skin conditions. However until now no solution to this problem has been found.
We have surprisingly discovered that desmosomal structures are present in the uppermost layers of the stratum corneum in dry flaky skin conditions, this is not the case in normal skin. Furthermore, we have been able to substantially solve the problem of dry flaky skin conditions by topical application of a skin care composition comprising stratum corneum chymotrypsin-like enzyme.